Potash froth flotation is a conventional process for recovering potash values from ore pulps. Potash ores mined in the United States and Canada normally contain between about 5-50 percent sylvite (KCl). Other components of potash ore can include carnallite, langbeinite, kieserite, halite (NaCl) and gangue materials. Most often the gangue materials found with sylvite ores include halite, clays, (e.g., montmorillonite) and gypsum along with minor amounts of iron oxides, manganese oxides and other minerals.
The siliceous gangue (i.e., clay) interferes with the recovery of potash values from potash-containing ores, whether the recovery is a flotation or heavy media separation or dissolution procedure. Thus, the deleterious effects of siliceous gangue during potash recovery are manifold. In flotation processes the slime-like gangue absorbs the expensive flotation agents. In differential settling in heavy media, the siliceous slime prevents efficient setting rates. In dissolution processing, the slime absorbs up to five times its weight in potash saturated brine and interferes with thickening and filtration.
A series of technical developments have addressed the problems characteristic of siliceous slimes which are present during the recovery of potash values from potash-containing ores. Mechanical means of desliming potash ores, which commonly employ equopment such as cyclones, filters and centrifuges, are non-selective and inefficient and result in an uneconomical loss of potash values.
U.S. Pat. No. 3,095,282 describes an improved process for recovering potash values from sylvinite ores which contain slime-forming clay. The process involves crushing the ore and dissolving the crushed ore in an aqueous brine solution, wherein the brine is saturated with respect to NaCl and unsaturated with respect to KCl. The KCl of the sylvinite ore dissolves in the brine solution and the NaCl of the sylvinite ore remains substantially undissolved, and the clay content of the ore remains suspended in the brine solution. The said brine solution containing suspended clay and undissolved NaCl is decanted, and to the decanted brine is added 0.0005-0.01 percent, based on the ore weight, of a flocculant selected from acrylic and methacrylic polymers. The suspended clay is caused to adhere to the undissolved NaCl, and it rapidly settles out to yield a substantially clear brine solution which contains dissolved potash values.
U.S. Pat. No. 3,782,546 describes a potash froth flotation process which involves the steps of grinding the potash ore, mixing the ground ore with brine to form an ore pulp, aerating the pulp to form a froth of potash values, and collecting and processing the froth. The improvement in the process consists of adding to the ore pulp prior to frothing a water soluble, high molecular weight diallyl dialkyl quaternary ammonium polymer as a blinding agent for the clay slime. The blinding agent selectively coagulates the slime.
U.S. Pat. No. 3,805,951 describes a process for desliming sylvinite ores by a selective flocculation and froth flotation of the slime. The process involves treating the ore pulp with a high molecular weight acrylamide polymer to flocculate the slime and then with a cationic collector for the flocculated slime. The treated ore pump is subsequently subjected to froth flotation to float off the flocculated slime.
There is continuing research effort to develop improvements in processes for separating potash values from sylvinite type of ores.
Accordingly, it is a main object of this invention to provide an improved process for improving the efficiency of potash recovery from sylvinite ores.
It is another object of this invention to provide a pretreatment procedure for the selective flocculation and froth flotation of the siliceous slime content of potash ores.
It is a further object of this invention to provide a novel combination of flocculant and collector agents for the desliming of potash ore pulp before the recovery of potash values.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.